What Causes Anaphylaxis

What Causes Anaphylaxis?

It’s an extreme response to an allergen.

A life‑threatening allergic reaction (anaphylaxis) is a severe reaction to a specific allergen, or allergic trigger. Common allergic triggers can include but are not limited to food, biting or stinging insects, medications and latex (expand below for details on each). Exercise‑induced anaphylaxis is also possible, and sometimes anaphylaxis has no apparent cause at all (this is known as idiopathic anaphylaxis).


Food allergy prevalence

Food allergies are on the rise, especially in children. As many as 8 million Americans, or 2.5% of the US population, have food allergies. The foods that most commonly cause anaphylaxis include:

  • Peanuts (the main cause of allergies in children)
  • Tree nuts (such as walnuts, pecans and cashews)
  • Shellfish (such as shrimp and lobster—the main cause of anaphylaxis in adults)
  • Fish
  • Cow’s milk
  • Eggs
  • Wheat
  • Soy

Severity is linked to many variables

The severity of a food‑triggered life‑threatening allergic reaction depends on a number of factors—the amount eaten, the food form (cooked, raw or processed) and the co‑ingestion of other foods. Other variables include the person’s age, the sensitivity at the time of ingestion, how fast the food is absorbed by the body and whether the person has another condition, such as severe or uncontrolled asthma.

Allergen avoidance means careful planning.

If you or your child has a food allergy, you’ll need to be careful to avoid allergic triggers. This means careful menu planning, avoiding cross‑contamination and reading food labels for alternative ingredient names to make sure you are aware of any “hidden” triggers.

Allergens aren’t always easy to avoid.

Food triggers can be difficult to avoid, particularly if the allergen is hidden in the meal or mislabeled in the ingredient list. In particular, children with potentially life‑threatening food allergies may inadvertently eat a trigger food at school. In this case, it’s important that the child and his/her family, caregivers and teachers know how to recognize the signs and symptoms of anaphylaxis and know what to do in the event of a life‑threatening allergic reaction: Administer the EpiPen® (epinephrine) or EpiPen Jr® (epinephrine) Auto‑Injector immediately and seek emergency medical care. Be prepared with an anaphylaxis action plan.

Insect Stings and Bites

The difference between a reaction and a potentially life‑threatening allergic reaction

Most people stung or bitten by an insect may experience swelling, pain and redness that may persist for up to a week and usually gets better without treatment. However, for those who have a life-threatening allergy to insect stings or bites, the situation may become life‑threatening.

If you’re one of those affected, consider taking these precautions:

  • When you go outside, avoid wearing brightly colored clothing or using sweet‑smelling lotions, perfumes and shampoos
  • Always wear shoes
  • If you’re eating, keep your food and trash tightly sealed
  • If your activity might expose you to insects or their nests (gardening or hiking, for instance), wear pants and long‑sleeved shirts

Avoid what you can.

Not all stings and bites can be avoided, so those with potentially life‑threatening insect allergies should have access to two epinephrine auto‑injectors, such as the EpiPen® (epinephrine) Auto‑Injector, particularly when outdoors.

Treating insect allergies

People with insect allergies can be treated with standardized insect injections (immunotherapy), which may provide long‑term protection against insect stings. However, not everyone treated this way remains tolerant to insect stings or bites for life. You may still need to carry an EpiPen 2‑Pak®.

In case of anaphylaxis triggered by insect bites or stings, administer the EpiPen or EpiPen Jr® (epinephrine) Auto‑Injector immediately and seek emergency medical care.



Medications are a common cause of anaphylaxis, with penicillin accounting for the most cases. Other drugs that can trigger anaphylaxis include aspirin, ibuprofen and cancer medications. Medication‑triggered anaphylaxis can occur in people of any age, but is particularly common in those middle‑aged and older. Your health care professional can help you recognize the symptoms of a severe medication allergy and assist in identifying other treatment options.

Keep track

To help ensure that you or your child is not prescribed a medication that will trigger anaphylaxis, keep a complete history of allergic reactions and the results of any diagnostic tests—and be sure to share it with your health care professional. You or your child should also wear a medical identification bracelet to alert health care professionals about your potentially life‑threatening allergies in case you can’t communicate.

In case of medication‑triggered anaphylaxis, administer the EpiPen® (epinephrine) or EpiPen Jr® (epinephrine) Auto‑Injector immediately and seek emergency medical care.


Who’s at risk?

Health care workers and other workers with occupational exposure to latex, as well as children with certain illnesses, including spina bifida and genitourinary abnormalities, are at higher risk of experiencing a life‑threatening allergic reaction.

Latex‑triggered anaphylaxis has been reported after exposure to latex‑containing gloves, condoms, rubber‑handled racquets, balloons, infant pacifiers and bottle nipples.

Treating a severe allergic reaction to latex

In case of latex‑triggered anaphylaxis, administer the EpiPen® (epinephrine) or EpiPen Jr® (epinephrine) Auto‑Injector immediately and seek emergency medical care.

Other Causes

Exercise‑induced anaphylaxis

Exercise‑induced anaphylaxis is a form of physical allergy with symptoms that include a warm feeling spreading throughout the entire body, itching and redness of the skin. Vigorous forms of physical activity, such as jogging, are more commonly associated with anaphylaxis, although lower levels of exertion (e.g., yard work) are also capable of triggering attacks.

Exercise‑induced anaphylaxis is often associated with medications or foods that have been taken or eaten prior to or after exercise. Someone with a history of exercise‑induced anaphylaxis due to foods should avoid exercising for four to six hours after eating. Exercise‑triggered anaphylaxis has a higher incidence in people genetically predisposed to developing allergic conditions.

Idiopathic anaphylaxis

When no triggers for anaphylaxis can be identified, a diagnosis of idiopathic anaphylaxis is made. If you or your child experiences anaphylaxis and the cause is unknown, your health care professional will analyze the events and conditions surrounding the allergic reaction so you can be careful to avoid possible triggers.

Like other forms of life‑threatening allergic reactions, a case of exercise‑induced or idiopathic anaphylaxis is treated with epinephrine. In case of exercise‑triggered or idiopathic anaphylaxis, administer the EpiPen® (epinephrine) or EpiPen Jr® (epinephrine) Auto‑Injector immediately and seek emergency medical care.

What happens inside the body when anaphylaxis occurs?

Anaphylaxis occurs when the body perceives a trigger as a threat and starts forming antibodies (special proteins made by the body’s immune system) to defend itself. These antibodies cause the release of certain molecules that produce the immediate symptoms of anaphylaxis.

Everyone—and every allergic reaction—is different.

Consult a health care professional if you or your child has had even a mild reaction to an allergen, because a mild reaction is not an indicator of the severity of future reactions. A mild allergic reaction can progress and become life‑threatening within minutes.

Getting tested for potentially life‑threatening allergens

In individuals who have experienced anaphylaxis, it is important to confirm the allergic trigger (or triggers). Several tests are available to help identify triggers of anaphylaxis:

  • Skin Tests identify allergies that may be a trigger for anaphylactic reactions, such as from food, medications and biting or stinging insects. In the case of a skin prick/puncture test, a positive result is indicated by the size of the inflammation when compared to placebo.
  • In Vitro Tests determine the presence of allergen‑specific antibody levels and identify anaphylactic reactions triggered by food, biting or stinging insects, medications and natural rubber latex.
  • Challenge Tests are incremental health care professional‑monitored tests to determine the clinical relevance of positive allergen skin tests or in vitro tests.

These tests can be done for children or adults. Test results alone do not diagnose allergies, so all test results must be interpreted together with your medical history. Your health care professional will determine which test, if any, is right for you.


EpiPen® (epinephrine) 0.3 mg and EpiPen Jr® (epinephrine) 0.15 mg Auto-Injectors are for the emergency treatment of life-threatening allergic reactions (anaphylaxis) caused by allergens, exercise, or unknown triggers; and for people who are at increased risk for these reactions. EpiPen and EpiPen Jr are intended for immediate self administration as emergency supportive therapy only. Seek immediate emergency medical treatment after use.

Important Safety Information

EpiPen Auto-Injectors contain a single dose of epinephrine, which you inject into your outer thigh. DO NOT INJECT INTO YOUR VEIN, BUTTOCK, FINGERS, TOES, HANDS OR FEET. In case of accidental injection, please seek immediate medical treatment. Epinephrine should be used with caution if you have heart disease or are taking certain medicines that can cause heart-related (cardiac) symptoms.

Tell your doctor if you have certain medical conditions such as asthma, depression, thyroid disease, Parkinson’s disease, diabetes, high blood pressure and heart disease, have any other medical conditions, are pregnant or plan to become pregnant, or are breastfeeding or plan to breastfeed. Be sure to also tell your doctor all the medicines you take, especially medicines for asthma. If you have certain medical conditions, or take certain medicines, your condition may get worse or you may have longer lasting side effects when you take the EpiPen or EpiPen Jr Auto-Injector.

The most common side effects may include increase in heart rate, stronger or irregular heartbeat, sweating, nausea and vomiting, difficulty breathing, paleness, dizziness, weakness or shakiness, headache, apprehension, nervousness or anxiety. These side effects usually go away quickly, especially if you rest.

Talk to your healthcare professional to see if EpiPen or EpiPen Jr Auto‑Injector is right for you.

Please see the full Prescribing Information and Patient Information.

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch or call 1‑800‑FDA‑1088.

For additional information, please contact us at 800‑395‑3376.

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